Rails Security

Rails Security Jonathan Weiss, 30.10.2009 Peritor GmbH

Who am I ? I work at Peritor in Berlin I tweet at @jweiss I code at http://github.com/jweiss I blog at http://blog.innerewut.de 2

Peritor Working on http://scalarium.com 3

Agenda Follow the application stack and look for Setup and deployment • Information leaks Application code • Possible vulnerabilities • Security best practices Framework code Rails Application Stack 4 4

Rails Application Setup 5

Rails Setup 6

Rails Setup - FastCGI 7

Rails Setup - Mongrel 8

Rails Setup – mod_rails 9

Rails Setup – Unicorn 10

Information leaks and vulnerabilities 11

Information leaks Is the target application a Rails application? • Default setup for static ﬁles: /javascripts/application.js /stylesheets/application.css /images/foo.png • URL schema /project/show/12 /messages/create /folder/delete/43 /users/83 12

Information leaks Is the target application a Rails application? • Rails provides default templates for 404 and 500 status pages • Different Rails versions use different default pages • 422.html only present in applications generated with Rails >= 2.0 • Dispatcher ﬁles not present in recent Rails versions 13

Sample Status Pages http://www.twitter.com/500.html http://www.43people.com/500.html http://www.engineyard.com/500.html Rails >= 1.2 status 500 page 14

Server Header GET http://www.haystack.com Date: Wed, 28 Oct 2009 11:23:24 GMT Server: nginx/0.6.32 Cache-Control: max-age=0, no-cache, no-store … GET https://signup.37signals.com/highrise/solo/signup/new Date: Wed, 28 Oct 2009 11:54:24 GMT Server: Apache X-Powered-By: Phusion Passenger (mod_rails/mod_rack) 2.2.5 Status: 200 OK … 15

Server Header GET http://www.twitter.com Date: Wed, 28 Oct 2009 11:23:24 GMT Server: hi Status: 200 OK … GET http://www.golfermail.org Date: Wed, 28 Oct 2009 11:13:41 GMT Server: Mongrel 1.1.5 Status: 200 OK … Disable Server header # httpd.conf Header unset Server Header unset X-Powered-By 16

Information leaks Subversion metadata • Typically Rails applications are deployed with Capistrano / Webistrano • The default deployment will push .svn directories to the servers GET http://www.strongspace.com/.svn/entries … dir 25376 http://svn.joyent.com/joyent/deprecated_repositories/www.strongspace/trunk/public http://svn.joyent.com/joyent Prevent .svn download 2006-04-14T03:06:39.902218Z <DirectoryMatch "^/.*/.svn/"> 34 ErrorDocument 403 /404.html justin@joyent.com Order allow,deny Deny from all … Satisfy All </DirectoryMatch> 17

Cookie Session Storage Since Rails 2.0 the session data is stored in the cookie by default Base64(CGI::escape(SESSION-DATA))--HMAC(secret_key, SESSION-DATA) 18

Cookie Session Storage Security implications • The user can view the session data in plain text • The HMAC can be brute-forced and arbitrary session data could be created • Replay attacks are easier as you cannot ﬂush the client-side session Countermeasures • Don’t store important data in the session! • Use a strong password, Rails already forces at least 30 characters • Invalidate sessions after certain time on the server side … or just switch to another session storage 19

Cookie Session Storage Rails default session secret Set HTTPS only cookies 20

Cross-Site Scripting - XSS “The injection of HTML or client-side Scripts (e.g. JavaScript) by malicious users into web pages viewed by other users.” 21

Cross-Site Scripting - XSS Cases of accepted user input • No formatting allowed search query, user name, post title, … • Formatting allowed post body, wiki page, … 22

XSS - No Formatting Allowed (Rails 2.x) Use the Rails `h()` helper to HTML escape user input But using `h()` everywhere is easy to forget. Better, use safeERB, XSS Shield, or rails_xss plugins: http://agilewebdevelopment.com/plugins/safe_erb http://code.google.com/p/xss-shield/ http://github.com/NZKoz/rails_xss 23

XSS - No Formatting Allowed (Rails 3) Rails 3 auto escapes strings in RHTML template Explicitly mark strings as HTML safe 24

XSS - No Formatting Allowed (Rails 3) rails_xss Plugin • Build-in in Rails 3 • Introduces “Safe Buffer” concept • Updates all the helpers to mark them as html_safe! • Requires Erubis Install and get familiar with if on Rails 2.x http://github.com/NZKoz/rails_xss 25

XSS - Formatting Allowed Two approaches Use custom tags that will translate to HTML (vBulletin tags, RedCloth, Textile, …) Use HTML and remove unwanted tags and attributes • Blacklist - Rails 1.2 • Whitelist - Rails 2.0 26

XSS - Custom Tags Relying on the external syntax is not really secure Filter HTML anyhow 27

XSS - HTML Filtering Use the Rails `sanitize()` helper Only effective with Rails > 2.0 (Whitelisting): • Filters HTML nodes and attributes • Removes protocols like “javascript:” • Handles unicode/ascii/hex hacks 28

XSS - HTML Filtering sanitize(html, options = {}) http://api.rubyonrails.com/classes/ActionView/Helpers/SanitizeHelper.html 29

XSS - HTML Filtering Utilize Tidy if you want to be more cautious 30

Session Fixation Provide the user with a session that he shares with the attacker: 31

Session Fixation Rails uses only cookie-based sessions Still, you should reset the session after a login The popular authentication plugins like restful_authentication are not doing this! 32

Cross-Site Request Forgery - CSRF You visit a malicious site which has an image like this Only accepting POST does not really help 33

CSRF Protection in Rails By default Rails > 2.0 will check all POST requests for a session token All forms generated by Rails will supply this token 34

CSRF Protection in Rails Very useful and on-by-default, but make sure that • GET requests are safe and idempotent • Session cookies are not persistent (expires-at) 35

SQL Injection The user’s input is not correctly escaped before using it in SQL statements 36

SQL Injection Protection in Rails Always use the escaped form If you have to manually use a user-submitted value, use `quote()` 37

SQL Injection Protection in Rails Take care with Rails < 2.1 Limit and offset are only escaped in Rails >= 2.1 ( MySQL special case ) 38

JavaScript Hijacking http://my.evil.site/ JSON response The JSON response will be evaled by the Browser’s JavaScript engine. With a redeﬁned `Array()` function this data can be sent back to http://my.evil.site 39

JavaScript Hijacking Prevention • Don’t put important data in JSON responses • Use unguessable URLs • Use a Browser that does not support the redefinition of Array & co, currently only FireFox 3 • Don’t return a straight JSON response, prefix it with garbage: The Rails JavaScript helpers don’t support prefixed JSON responses 40

Mass Assignment User model 41

Mass Assignment Handling in Controller A malicious user could just submit any value he wants 42

Mass Assignment Use àttr_protected` and àttr_accessible` Vs. Start with àttr_protected` and migrate to àttr_accessible` because of the different default policies for new attributes. 43

Rails Plugins Re-using code through plugins is very popular in Rails Plugins can have their problems too • Just because somebody wrote and published a plugin it doesn’t mean the plugin is proven to be mature, stable or secure • Popular plugins can also have security problems, e.g. restful_authentication • Don’t use svn:externals to track external plugins, if the plugin’s home page is unavailable you cannot deploy your site 44

Rails Plugins How to handle plugins • Always do a code review of new plugins and look for obvious problems • Track plugin announcements • Track external sources with Piston, a wrapper around svn:externals http://piston.rubyforge.org/ 45

Conclusion 46

Conclusion Rails has many security features enabled by default • SQL quoting • HTML sanitization • CSRF protection The setup can be tricky to get right Rails is by no means a “web app security silver bullet” but adding security is easy and not a pain like in many other frameworks 47

Questions? 48

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Rails Security

by Jonathan Weiss on Oct 30, 2009

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Rails Security — Presentation Transcript